Sensor Technology for Radiotherapy Monitoring

Dr. Sinéad O'Keeffe, Research Fellow, Optical Fibre Sensors Research Centre, University of Limerick, talks to AZoSensors about Sensor Technology for Radiotherapy Monitoring.

How do your new sensors work to enhance patient safety in radiotherapy?

The sensor uses optical fibre sensing technology and is based on radio-luminescence. A plastic optical fibre is coupled with a radiation sensitive material, which fluoresces under ionising radiation, such as those used in radiotherapy. The emitted optical signal penetrates the fibre and propagates along the fibre where it is remotely monitored.

Optical fibre sensors offer numerous advantages over conventional dosimeters, such as thermoluminescence dosimeters (TLDs) and semiconductor diodes. The small dimensions of the optical fibre dosimeter make them suitable for minimally invasive in vivo applications.

This would allow the radiation dosimeter to be placed either directly into or in close proximity to the tumour, or in the case of a brachytherapy implant alongside the dose delivering implantable seeds, or radioactive sources, in a manner which has not been previously achieved in order to provide real-time dosimetric information (e.g., in close proximity to the implants in the tumour itself or critical tissues requiring monitoring).  

During your work on the development of sensor technology over the past nine years, what changes have been made to this technology to diversify the application of sensors in radiotherapy?

Our initial work in the development of radiation dosimeters focussed on high dose applications, such as those found in the sterilisation and nuclear industries. However, demands from advances in radiotherapy resulted in the divergence of the sensor to clinical applications. The sensor has evolved, by using radiation sensitive materials in conjunction with the fibre for improved sensitivity and is now capable of monitoring very low doses of radiation, such as those found in radiotherapy.

Advances in detection optics have also allowed us to improve the sensitivity of the sensor for low dose applications.

How do you ensure the safety of surrounding tissue when applying these sensors during radiotherapy treatment?

In vivo dosimetry directly monitors the radiation dose delivered to a patient during radiation therapy. It allows comparison of prescribed and delivered doses and thus provides a level of radiotherapy quality assurance that supplements computational double checks.

A well-devised in vivo dosimetry program provides additional safeguards without significantly extending treatment delivery time. By placing the sensor at critical points on the patient, for example close to the tumour, we can monitor the amount of radiation the patient is receiving. The results are in real-time and so immediate knowledge of the radiation dose can ensure the safety of the patient.  

One of the most commonly occurring clinical complications, arising from radiation treatments of the pelvic region, are a result of a high dose delivered to the portions of the rectum and bladder that are in close proximity to the tumour. Knowledge of the radiation dose to critical structures is necessary to ensure that side-effects can be minimised, while maintaining an adequate standard of treatment. These internal doses are traditionally calculated as part of the treatment planning process. Our optical fibre sensors will allow for minimally invasive in-vivo measurements providing exact information on the radiation dose received to these critical organs.

What output data is recorded from these sensors to indicate the levels of radiation exposed to critical organs?

The sensor emits visible light dependant on the amount of input radiation received. By continuously monitoring the optical signal from the sensor in real-time we can determine the radiation dose the patient receives.

How does this technology compare to current technologies aiming to monitor critical organ tissue during radiation?

Traditional methods for estimating the dose delivered during radiation treatment have involved the use of detectors placed on the patient’s skin to monitor the actual dose delivered in comparison to that planned. Our technology is smaller than currently available sensors and making them suitable for minimally invasive in vivo monitoring.

The dosimetric information provided is similar to that of current technology; however, by placing the sensor in close proximity to the tumour or at critical organs, dosimetric information at these critical points can be monitored directly.

Are there any limitations with this new technology?

The sensor is still in its early stage of development and so the extent of the sensor’s limitation has yet to be fully explored. To date we have not encountered any limitation that we cannot overcome through small adaptations to the sensor system design.

What factors will be monitored to improve patient safety when using this technology?

The sensor monitors the radiation dose that a patient receives. It is capable of monitoring in real-time and so the instantaneous radiation and the accumulative dose is provided.  By providing real-time information of the radiation levels and dose that a patient is exposed to, it is possible to alert hospital personnel to possible high radiation exposure to critical structures in the body in advance of it becoming an issue.

How has your work with Marie Curie Research on the development of radiation dosimeters helped advance areas of real-time patient monitoring with regard to radiation treatment?

The Marie Curie Research Fellowship, funded by the European Commission under the 7th Framework Programme through the ‘Marie Curie Re-integration’ action of the ‘Peoples’ Programme (PERG04- 2008-239207), has allowed for this sensor technology to be developed. Without the financial support of this programme, the research would not have been successful in progressing to this stage.

How do you see this sensor technology developing in the field of radiation therapy?

Optical fibres offer a number of advantages over current sensing technologies for specific applications areas within the field of radiation therapy. The small dimensions of the optical fibre dosimeter make them particularly suitable for minimally invasive in vivo applications. In addition to the previously discussed application of internal monitoring critical organs or the tumour itself, the small sensor makes it particularly suitable for Brachytherapy applications. Brachytherapy involves the positioning of radioactive sources in, or near to, the tumour.

A common type of brachytherapy treatment involves the introduction of small ‘seeds’, containing radioactive Iodine-125, directly into the prostate using long needle-like applicators. The small dimensions of the sensor would allow it to be placed alongside the seeds, or radioactive sources, in a manner which has not been previously achieved, to provide real-time dosimetric information.

Recent advances in this state-of-the-art technology have resulted in the emergence of radiotherapy beam delivery systems (Linear Accelerators or Linacs) combined with MRI (magnetic resonance imaging) in a single system. Optical fibres generally comprise only silica (glass) or plastic as their constituent material; therefore, optical fibre sensors are uniquely and ideally suited for use in the MRI environment as they are non-magnetic and do not cause interference on the image and are themselves immune to the intense magnetic field and radio frequency pulses present in the MRI environment.

How do you feel about recently being awarded the Institute of Electrical Engineering and Electronics Sensors Council Early Career (GOLD) Award? How do you plan on continuing to merge the field of sensor technology in other areas of medicine?

It was a huge honour to receive the award from the IEEE Sensors Council and is a credit to the whole team at the Optical Fibre Sensors Research Centre and our collaborators involved in this research.

The Optical Fibre Sensors Research Centre at the University of Limerick is involved in a number of projects developing optical sensors for a range of medical applications, such as cardiac monitoring, lung and bladder pressure sensing and monitoring the curvature of the spine for physiotherapy applications.   

Where can we find further information on your work?

Further information on the radiotherapy dosimeter and other medical sensors currently being developed by the Optical Fibre Sensors Research Centre can be found by visiting our website at www.ofsrc.ul.ie  

About Dr. Sinéad O'Keeffe 

Dr. Sinéad O'Keeffe received her PhD in 2006 from the University of Limerick, for the development of polymer optical fibre sensors for the sterilization industry. On completion of her PhD, she worked as a Marie Curie Research Fellow in the General Engineering Research Institute at Liverpool John Moores University, developing optical fibre sensors for monitoring UV and Ozone.

She returned to the Optical Fibre Sensors Research Centre at the University of Limerick and was awarded an FP7 Marie Curie Research Fellowship developing radiation dosimeters for monitoring patient doses received during radiotherapy for cancer treatment. She is Chair of a pan-European COST Action TD1001 “OFSeSa”, aimed at developing fibre optic sensor systems for reliable use in safety and security relevant applications in society.